Contains FAD as prosthetic group. One of several enzymes that catalyse the first step in fatty acids β-oxidation. The enzyme catalyses the oxidation of saturated short-chain acyl-CoA thioesters to give a trans 2,3-unsaturated product by removal of the two pro-R-hydrogen atoms. The enzyme from beef liver accepts substrates with acyl chain lengths of 3 to 8 carbon atoms. The highest activity was reported with either butanoyl-CoA [2] or pentanoyl-CoA [4]. The enzyme from rat has only 10% activity with hexanoyl-CoA (compared to butanoyl-CoA) and no activity with octanoyl-CoA [6]. cf. EC 1.3.8.7, medium-chain acyl-CoA dehydrogenase, EC 1.3.8.8, long-chain acyl-CoA dehydrogenase, and EC 1.3.8.9, very-long-chain acyl-CoA dehydrogenase.